The outlet end of a combustion chamber wall, in particular the outlet end of an external wall of the combustion chamber of a gas turbine combustion chamber (also called aft end) heats up substantially more slowly during the starting process than the remainder of the combustion chamber wall. During the starting phase, the slower heating up leads to a smaller thermal expansion of the combustion chamber wall at its outlet end compared to the remaining regions. If the external wall is divided, then the outlet end can be drawn inward due to the different heating up. On account of the varying thermal expansion, deformations result that can in turn lead to high mechanical stresses on the outlet end. For example, the smaller thermal expansion of the outlet end in a rotationally symmetrical combustion chamber with a circular outlet end leads to a constriction on the outlet end and for this reason to an ovalization of the combustion chamber cross section on the outlet end.
The high stresses arising due to the uneven deformation can in particular in the transition section between the outlet end and an adjacent region with passage openings for the passage of compressed air of the compressor mass air flow through the combustion chamber wall, damage the supporting structure thereof.
There is also the fact that axially symmetrical combustion chambers usually have external wall of the combustion chambers embodied in two parts, which are screwed to one another along an axial external line by means of screws. The high mechanical stresses developing when starting the gas turbine in the transition region between the outlet end and the remainder of the combustion chamber wall can exceed the load limit of the screw situated directly on the outlet end. Therefore, this screw can be exposed to enormous bending loads, which at the end of the day can lead to the destruction of the screw.
In addition, the turbine guide vanes of the first vane ring of the turbine are frequently integrated in the outlet end of the combustion chamber, for example by being screwed to the outlet end of combustion chamber walls, in particular to the outlet end of external wall of the combustion chambers. A deformation of the outlet end leads to a shift of these guide vanes. For example, the turbine blades in an annular combustion chamber, in the case of which the above-mentioned ovalization occurs, would shift in a radial manner according to the ovalization. Therefore, provision must be made for a large gap between the outlet end and the guide vanes in order that the guide vanes can shift and for this reason that the blades do not knock against the housing. In this process, the size of the gap is measured in accordance with the deformations of the outlet end occurring during the transient conditions of the gas turbine installation and in particular when starting the gas turbine installation. However, a large gap causes problems when creating a seal concept within the transition region between the turbine guide vanes and the combustion chamber wall, which must be taken into account in the case of the seal concept. Besides, a large gap means that a relatively large amount of working medium of the gas turbine installation can exit the combustion chamber via the gap. Since the exiting working medium for propelling the turbine is lost, a large gap reduces the efficiency of the gas turbine installation.